1. Field of the Invention
The present invention relates to measurement of bit error rate in communication systems and circuits.
2. Description of Prior Art
So far as is known, prior art error detection systems were of two general types: closed loop systems and open loop systems.
In closed loop systems, such as in U.S. Pat. Nos. 3,916,379 and 3,934,224, the signal as sent by a communication system under test was compared with the signal as received, requiring a signal path in addition to the one for the system under test. Thus with closed loop systems, bit error rate measurement of radio frequency (RF) communication links was difficult.
With open loop systems, such as in U.S. Pat. No. 3,914,740, a distinctive, self-identifying, pseudo-random noise (PRN) sequence was used as a test signal and sent over a communication link to the system under test. A replica of the PRN sequence was formed at the receiver of the system under test and compared with the PRN sequence received over the communication link under test. However, this type of system required a relatively "clean," i.e., low noise, communication link and was thus not suitable for bit error rate testing of low signal-to-noise radio communication systems and links. Further, since bit-by-bit comparison required bit synchronization between the received PRN sequence and its replica, bit error rate testing became difficult when the bit rate neared the tracking threshold of the bit synchronizer.